Control valves are utilized in a variety of industrial applications for regulating gases and liquids. One particularly good example is the steam control valve for turbines of a nuclear power plant. Such valves are in fluid communication with steam coming from the steam generator and usually include a cylindrical plug which controls the flow of steam through the turbine. The plug reciprocally slides within a bonnet disposed within the valve body to permit steam flow. Also disposed within the valve body, is usually a noise-suppressing valve cage, or "muffler," having multiple circular apertures, e.g., about 1000 holes 5/16 inches (0.79 cm) I.D., and a series of large window openings. The muffler both guides the valve plug and attenuates valve flow noise. Valve and muffler systems which are relevant in this regard are described in Connors, et al., U.S. Pat. No. 4,705,071, 11/10/87; Brown, et al., U.S. Pat. No. 3,602,261, 8/31/71; and Heymann, et al., U.S. Pat. No. 4,766,932, 8/30/88, which are all hereby incorporated by reference.
Connors, et al. discloses an improved muffler portion design including a plurality of flow pockets, with a flow pocket aligned with the large window openings. This design is stated to reduce vibrations which can damage the valve.
Heymann, et al. discloses an improved steam control valve largely directed to reducing the effect of vibrational excitations experienced during steam throttling. The valve plug of this reference is guided by a substantially rigid cylindrical bushing for reducing vibration.
Brown discloses an early steam control valve which incorporates a valve cage with a muffling device for reducing noise and vibration.
Although control valve structures have been disclosed for reducing the high levels of noise associated with the flow of high-pressure steam in modern steam turbines, there remains a need for a more uniform hole arrangement within the muffler for minimizing deadband and providing a more gradual increase in steam flow as a function of valve lift for minimizing vibration and noise.